1. Field
The present disclosure relates to a light sensing circuit having a simplified structure using an oxide semiconductor transistor capable of sensing light as a light sensing device, a light sensing apparatus including the light sensing circuit, a method of driving the light sensing apparatus, and an image acquisition apparatus and optical touch screen apparatus including the light sensing apparatus.
2. Description of the Related Art
Touch screen devices are devices which may directly receive input data through a screen by recognizing a position of, for example, a finger, a stylus, or the like, touching the screen and performing a particular process by a software routine. To this end, a touch screen device may be equipped with a touch panel to perform the above function. Such touch panels may include resistive overlay type touch panels, capacitive overlay type touch panels, surface acoustic wave (SAW) type touch panels, infrared beam type touch panels, piezoelectric type touch panels, or the like. The touch screen device is widely used in a variety of fields as an input device replacing a keyboard or a mouse.
A touch screen device that has been widely used employs a method of directly touching a screen of a display device using a finger or a stylus. However, as the size of a display device increases, the distance between the display device and a user may increase. In this case, use of the direct touch method may be difficult to adopt. Accordingly, optical touch screen devices have been proposed that may perform the same function as the existing touch screen by sensing light instead of sensing contact of a finger or a stylus. An optical touch screen device may facilitate communications not only between a user and a terminal but also between a user and a user.
In order to realize such an optical touch panel, a relatively small sized light sensing device for sensing light may be required. An amorphous silicon thin film transistor (a-Si TFT) is one of generally used light sensing devices. However, an a-Si TFT may not exhibit a sufficient current change according to light. Accordingly, when light is incident, electric charges generated in a photodiode are accumulated in a capacitor for a predetermined period of time and then a signal related to light intensity may be generated from the quantity of electric charges accumulated in the capacitor. When a capacitor is used as above, a sensing time may be delayed as long as the time for accumulating electric charges in a capacitor. Also, as the size of an optical touch screen device increases, parasitic capacitance may increase as well.